The present invention is related to a method and a device for controlling an actuator unit, in particular to an actuator unit for a conveyor, and more particularly to an actuator unit for a conveyor for loading of a cargo compartment, in particular that of an aircraft fuselage. Such a loading conveyor or sliding carpet system is described in U.S. Pat. No. 4,984,756 (Helmner), which hereby is incorporated by reference.
The loading system is located beneath the passenger cabin and comprises a carpet-like conveyor, driven by an actuator unit via belts connected to the conveyor. A rear cargo wall is fixed to the belts and provides a rear storage room limit.
The loading system is used in the loading mode as follows:
The actuator unit is achieved and drives the rear wall to the front of the loading system.
One layer of suitcases or similar cargo is put down on the carpet-like conveyor.
The actuator unit is activated and drives the conveyor and the rear wall about half a meter backwards.
A new layer of cargo is put down on the conveyor and the actuator unit is again activated and the conveyor is loaded with another layer of cargo stepwise, until the conveyor is fully loaded, i.e. when the rear wall is at its most rearward position.
When the loading conveyor is to be unloaded the procedure is performed the other way around. The loading conveyor is stepwise unloaded and stepwise driven by the actuator unit until it is completely emptied, i.e. when the rear wall is in its most forward position.
The actuator (motor and gearbox) of the sliding carpet system typically consists of a three-phase electrical asynchronous motor connected to a reduction gear, e.g. a planet reduction gear. The rotational speed and torque of the actuator is dimensioned to handle/stand up to the highest specified baggage weight (maximum load) of the loading system. Also the electric system is dimensioned on basis of the maximum current consumption required by the actuator (asynchronous motor) at this maximum load.
The motor is protected by electric fuses or circuit breakers, which are blown or released at too high current, i.e. if the motor torque exceeds the maximum load. The fuses that protect the motor, the electric cables and other electric components are dimensioned on the basis of said maximum load of the conveyor. To protect the mechanical components, the movable bulkhead has release connections, which are released if the bulkhead hits a stop. These release connections must, after they have been released, be restored manually, which is a problem. It takes time, the sliding carpet must be unloaded manually, mechanics are to be called, and the function is only optimal in some loading cases.
The wiring of a typical prior art conveyor is shown in FIG. 2. The operator maneuvers the conveyor via a maneuver panel which transmits an actuator signal to a relay (15) which in turn determines if the actuator unit (16) is to be fed with the electric power or not. If something gets stuck, the release connections are released or the electric fuses are blown or released.
Maximum load is however very seldom reached for the reasons below:
The motor is dimensioned for use in different models and lengths (i.e. baggage weights) of the loading system; thus the motor is in many cases overdimensioned in respect of the maximum load of the actual sliding carpet system in which the motor is installed.
In many cases the maximum allowed baggage weight is not utilized, even when the cargo compartment of the airplane is fully loaded.
As loading and unloading is made step by step, only the inner step carries full load. Thereafter the load on the actuator is reduced down to zero at the last step.
This means that the actuator in most loading cases has a considerably larger pulling (i.e. torque) capacity than necessary. However, it must of course stand up to the maximum load at the innermost loading and unloading step, by which the sliding carpet system carries maximum load derived from the baggage weight.
The problem is that if the loading system hits some kind of stop, for example if the cargo net is not properly removed or if some baggage gets stuck, the electric fuses and the release connections as the bulkhead usually are not released fast enough, and they are in many cases overdimensioned in order to meet the maximum load requirements. Therefore, there is a risk that the loading conveyor with the sliding carpet system damages the baggage that gets stuck, or even gets damaged itself, whenever the loading conveyor is used with a load less than the maximum load. Furthermore every problem with damaged baggage or damaged loading conveyors leads to time consuming repairs or manual loading and unloading.
Another problem associated with known loading conveyors of the above mentioned type is incorrect operation of the loading conveyor by the operator. For instance, it is not that unusual that the operator maneuvers the loading conveyor in the unloading direction and lets the loading conveyor and the rear wall push the bags out of the loading compartment instead of lifting off the bags and maneuver the loading conveyor stepwise. Since the electrical wiring is dimensioned on the basis of the maximum load usually takes some time before the loading conveyor is stopped even if something gets stuck, when the loading conveyor is incorrectly operated. If something gets stuck it is usually the rear wall that is released, which means that the complete loading compartment must be unloaded manually and then the release connections of the rear wall must be reset. This manual unloading and reconnection of the release connections are quite time consuming.
In the field of air traffic, the time on the ground must be minimized to make a profit on the very costly investments of buying the planes and building the airports.
In the field of air traffic, the time on the ground is almost always determined by the time required for refueling, safety check and similar flight critical factors. It is never acceptable that the baggage loading system takes more time than the flight critical measures taken on the ground.
Thus it is not acceptable that the loading conveyor must be unloaded manually if something temporarily gets stuck or if the loading conveyor is incorrectly used.
Thus, an object of the invention is to eliminate or at least diminish the risk that a loading conveyor damages its environment, the cargo, the operator or itself if something gets stuck.
Another object of the invention is to prevent the operator from damaging the loading conveyor or its environment by incorrect operation of the sliding carpet system.
Another object is to reduce the time required to get the loading conveyor back in use after something has been temporarily stuck or after it has been incorrectly used.
These objects are achieved with a method for controlling the operation of an actuator unit, comprising the steps:
a) repeatedly reading the current fed to the actuator unit,
b) making a first comparison, wherein the readings are compared with a first maximum level and, if the readings are above said maximum level a number of times exceeding a maximum level stop number, the electric power fed to the actuator unit is cut off,
c) making a second comparison, wherein two successive readings repeatedly are compared with each other and, if the differences between the readings are below a first ramp level a number of times exceeding a steady state counter number, a steady state condition for the current fed to the actuator unit is detected.
d) if steady state is detected, setting at least one overload detection limit on the basis of at least one steady state reading of the current fed to the actuator unit.
By initially comparing the current with the maximum level and detecting steady state and finally setting one or more overload detection limits on the basis of the steady state current, the method manages to control an actuator unit with varying load conditions and still cut the power fast enough if something gets stuck. Even if the actuator unit drives, for instance, a conveyor with a load far from the maximum load of the conveyor the method cuts the power, not seldom long before the ordinary fuses or circuit breakers of known type are released, if something gets stuck.
According to a preferred embodiment of the inventive method, the method further comprises a step: e) making a third comparison, wherein the readings repeatedly are compared with a soft maximum level set on the basis of said steady state reading of the current and, if the reading exceeds said soft maximum level a number of times exceeding a soft maximum stop level number, the power fed to the actuator unit is cut off.
By setting a soft maximum level, the method cuts the power if the current slowly increases over a longer period of time. This might be the case when something begins to get stuck and the problem in question propagates but a real stop has not yet come up.
According to a preferred embodiment of the inventive method, the method further comprises a step: f) making a fourth comparison, wherein consecutive readings repeatedly are compared with each other and, if the differences between the readings repeatedly are above a second ramp level, the electric power fed to the actuator unit is cut off.
By comparing the readings with each other like this the method cuts the power even if a maximum level has not been reached. This means that if something gets stuck hard, the actuator unit is stopped almost immediately.
According to a further preferred embodiment of the inventive method, the first comparison step comprises the steps of comparing the readings with a first predetermined maximum level and, if the readings consecutively are above said maximum level a number of times exceeding a predetermined maximum level stop number, cutting the electric power fed to the actuator unit.
With this embodiment the quality of the method is increased, i.e. the method cuts the power more accurately in situations where the power is meant to be cut and does not cut the power when it is not meant to be cut.
According to a further preferred embodiment of the inventive method, the second comparison step comprises the steps of repeatedly comprising two consecutive readings with each other and, if the differences between the readings consecutively are below a first predetermined ramp level a number of times exceeding a predetermined steady state indicating level, detecting a steady state condition for the current fed to the actuator unit.
Also with this embodiment the quality of the method is increased, i.e. the method cuts the power more accurately in situations where the power is meant to be cut and does not cut the power when it is not meant to be cut.
According to a further preferred embodiment of the inventive method, the fourth comparison step comprises the steps of repeatedly comparing consecutive readings with each other and, if the differences between the readings are above a second predetermined ramp level a number of times exceeding a predetermined ramp indicating level cutting the electric power to the actuator unit.
With this embodiment the quality of the method is increased, i.e. the method cuts the power more accurately in situations where the power is meant to be cut and does not cut the power when it is not meant to be cut.
According to a further preferred embodiment of the inventive method, the soft maximum level is updated on the basis of the steady state readings of the current fed to the actuator unit.
With the embodiment the method takes into consideration any expected increase or decrease of the current during the period of time the actuator unit is activated. By updating the soft maximum level, the soft maximum level can be set closer to the actual reading of the steady state current and the accuracy of the method is increased.
According to a further preferred embodiment of the inventive method, the current fed to the actuator unit is read by way of a non-contacting method.
By using a non-contacting way of reading the current, it is easier to install a device incorporating the method in an existing installation.
According to a further preferred embodiment of the inventive method, the reading is conducted with a meter responding to the electromagnetic field around an electrical wire by which the actuator unit is fed with electrical power.
This is a safe and certain way of non-contractingly determining the current fed to the actuator unit.
The objects of the invention are also achieved with a device, for controlling the operation of an actuator unit, comprising:
an electrical current meter, repeatedly reading a current fed to an actuator unit,
a processing unit, which on one hand compares the readings with a maximum level and on the other hand compares the readings with each other and outputs a signal whether the actuator unit should be fed with electric power or not, and
an electrical switch, which receives the signal from the processing unit and relays or cuts off the electric power to the actuator unit.
By using a device of this type the behavior of the actuator unit is measured by the meter and taken into consideration in the processing unit and then controlled by the switch. By measuring the behavior of the actuator unit, limit values for the actuator unit can be set on the basis of different load situations and different behavior of the actuator unit and the environment driven by or otherwise influencing the actuator unit. This adaptive way of setting limits makes it possible for the device to cut the power to the actuator unit if something gets wrong, even if the maximum load of the actuator unit is not reached. This device controls the actuator unit even at loads far from the maximum load. The adoptively set limits can be much closer to the actual load situation than limits set on the basis of the maximum load, which means that the actuator unit is stopped if something goes wrong irrespectively whether the maximum load is reached or not.
According to a preferred embodiment of the inventive device, said signal-receiving electrical switch maneuvers a relay which maneuvers the actuator unit.
By using a two stage switching of the power, the risk of burning or damaging the device is highly diminished. The switch is maneuvered by a signal from the processing unit and transmits a signal of moderate voltage to the relay which in turn maneuvers electric drive power which often is too high for the first electric switch to handle. The choice of combinations of switches and relays is of course highly dependent on the environment in which the device is meant to be installed.
According to a preferred embodiment of the inventive device, the meter is a non-contacting meter, preferably an inductive meter reading the electromagnetic field around at least one of the conductors feeding the actuator unit with electric power.
According to a preferred embodiment of the inventive device, the meter, the processing unit and said signal-receiving switch are integral in a unit.
By integrating said components to an integral unit, installation and manufacture are highly facilitated.
The objects of the invention are also achieved with a conveyor incorporating a device, controlling the operation of an actuator unit of the loading conveyor, the device comprising:
an electric current meter, repeatedly reading a current fed to an actuator unit,
a processing unit, which on one hand compares the readings with a predetermined value and on the other hand compares the readings with each other and outputs a signal whether the actuator unit should be fed with electric power or not, and
a relay, which receives the signal from the processing unit and relays or cuts off the electric power to the actuator unit.
By using a device of said type in a conveyor, the safety of the operator, the load and the conveyor itself is highly enhanced. By using a device of this type the behavior of the actuator unit and thus the conveyor is measured by the meter and taken into consideration in the processing unit and then controlled by the switch. By measuring the behavior of the actuator unit, limit values for the actuator unit can be set an the basis of different load situations and different behavior of the actuator unit and the environment driven by or otherwise influencing the actuator unit. This adaptive way of setting limits makes it possible for the device to cut the power to the actuator unit if something gets wrong, even if the maximum load of the actuator unit is not reached. This device controls the actuator unit even at loads far from the maximum load. The adoptively set limits can be much closer to the actual load situation than limits set an basis of the maximum load, which means that the actuator unit is stopped if something goes wrong irrespectively of whether the maximum load is reached or not.
It should be noted that the features of the preferred embodiments of the inventive method and the inventive device can be combined in any desired way.